fix(done): use ResolveHookDir for dispatcher lookup (sc-g7bl3)

When a polecat runs gt done after work is complete, it should notify the
dispatcher (the agent that slung the work). This notification was failing
silently when the polecat's worktree was deleted before gt done finished.

The issue was that getDispatcherFromBead() used ResolveBeadsDir(cwd) which
relies on the polecat's .beads/redirect file. If the worktree is deleted
(e.g., by Witness cleanup), the redirect file is gone and bead lookup fails.

Fix: Use ResolveHookDir(townRoot, issueID, cwd) instead. ResolveHookDir uses
prefix-based routing via routes.jsonl which works regardless of worktree
state. This ensures dispatcher notifications are sent reliably even when
the worktree is cleaned up before gt done completes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/cmd/done.go

@@ -456,7 +456,7 @@ notifyWitness:
 
 	// Notify dispatcher if work was dispatched by another agent
 	if issueID != "" {
-		if dispatcher := getDispatcherFromBead(cwd, issueID); dispatcher != "" && dispatcher != sender {
+		if dispatcher := getDispatcherFromBead(townRoot, cwd, issueID); dispatcher != "" && dispatcher != sender {
 			dispatcherNotification := &mail.Message{
 				To:      dispatcher,
 				From:    sender,
@@ -678,12 +678,19 @@ func getIssueFromAgentHook(bd *beads.Beads, agentBeadID string) string {
 
 // getDispatcherFromBead retrieves the dispatcher agent ID from the bead's attachment fields.
 // Returns empty string if no dispatcher is recorded.
-func getDispatcherFromBead(cwd, issueID string) string {
+//
+// BUG FIX (sc-g7bl3): Use townRoot and ResolveHookDir for bead lookup instead of
+// ResolveBeadsDir(cwd). When the polecat's worktree is deleted before gt done finishes,
+// ResolveBeadsDir(cwd) fails because the redirect file is gone. ResolveHookDir uses
+// prefix-based routing via routes.jsonl which works regardless of worktree state.
+func getDispatcherFromBead(townRoot, cwd, issueID string) string {
 	if issueID == "" {
 		return ""
 	}
 
-	bd := beads.New(beads.ResolveBeadsDir(cwd))
+	// Use ResolveHookDir for resilient bead lookup - works even if worktree is deleted
+	beadsDir := beads.ResolveHookDir(townRoot, issueID, cwd)
+	bd := beads.New(beadsDir)
 	issue, err := bd.Show(issueID)
 	if err != nil {
 		return ""